Fairlife Followup

Last week I wrote the bottle that contains Fairlife chocolate milk and in particular about how confusing the recycling code at the bottom is. It's the number 7, but instead of saying "other" as it should, it says "PETE" (which corresponds to the number 1 code). I contacted Fairlife about this and received the following email:

"Hi John!

Thanks so much for reaching out; we REALLY appreciate your taking the time to get in touch with us.

Our bottles are primarily made from PET, which is #1 plastic. We add a very small percentage of white colorant to protect the milk from UV and visible light (UV and visible light impact the integrity of the milk and the vitamins present in it). The addition of the white colorant is what makes the plastic bottle #7. PET plastic and the white colorant are both approved by the FDA as safe for packaging food products. There is no BPA in any of our packaging.

If you have any other questions or comments, please do not hesitate to give us a shout!

All the best,

Brooke
Consumer Affairs

fairlife� ultra-filtered milk"

(Glad to see that the exclamation point key on their computer works so well!)

This just doesn't add up. Adding white colorant to PET doesn't make it a number 7, just as adding any other pigment to any other plastic doesn't change the base polymer or its recyclability.

But I question the need for a pigment at all. While Brooke is correct that the white plastic will "protect the milk from UV and visible light", a white pigment isn't needed. The bottle is already mostly covered in a brown-colored overwrap film which will block light. Besides, "normal" milk is packed in high-density polyethylene (HDPE) which is a hazy white without any white additives. The whiteness arises from the crystals in the material scattering light (which coincidentally is also why milk appears white).

(As an aside, UV absorbers have been added to polyethylene milk bottles, but understandably, consumers are put off by the yellow color. This is hardly new technology, having been around since at least 1993.)

My guess: there is a barrier layer in the package which makes the whole mess incompatible with PET, and that the white pigment story is just a red herring.

Previous Years

July 22, 2011 - The Heat Index and Jenson's Inequality

July 22, 2010 - A Bio-based Acrylic

Living Hinges

One mechanical entity that is almost exclusively limited to being constructed from polymers is a "living hinge". Trying to describe a living hinge can be difficult, so let me provide a few pictures of living hinges you might have around the house:

What American home doesn't have a ketchup bottle or two?

Fish sauce bottle

The common feature in all cases is that there is a thin strip of the polymer that provides a flexible, continuous (usually) hinge between two other more substantial parts. Trying to make such a hinge from metal would be pretty challenging (let alone ceramics or other rigid materials).

Living hinges are most commonly produced from polypropylene (PP) and polypropylene copolymers, not only because that material is plenty cheap, but also because when properly made, the hinges can last for years. I have a large polypropylene tub that originally was used for dog food some 12 years ago. It has since been repurposed for storing bird seed in an icy-cold/sultry-hot Minnesota garage. It has been flexed two or three times a week for its entire life, and other than where mice tried chewing through it last winter looking for some free seeds, it still works beautifully.

Last week when helping out with the laundry, I ran into a living hinge that I thought was a little unusual. It's a container for Tide Pods:

Tide Pods Container

I say it is unusual because the container is polyester. While polyester (PET) is used for living hinges, it's usually for food packaging such as this:

Fresh Mint

or other items at the grocery store. PET is much more expensive that PP, but it is used in food packaging because its clarity shows off the food so well. But that argument doesn't hold up with the PET used for the Tide Pods as it is not clear at all. Additionally, the hinge will be flexed quite a bit - the container holds 72 pods so that is at least 72 cycles of opening and shutting. So why does P & G use PET instead of PP? I have no idea. Perhaps some other aspect of the molding (cycle time for instance) dominates and allows for the use of a more expensive resin.

The term "living" hinge has always bothered me as there is nothing alive about the hinge. It's a hinge. A thin plastic hinge. But misuse of the word "living" in polymer science and engineering is nothing new. Look at "living" polymerizations. In a living polymerization, the polymerization reaction runs until the monomer is depleted, but unlike with more common reactions, the termination reaction never kicks in to permanently halt the polymerization. If more monomer is added to a depleted living polymerization, the reaction can pick up right where it left off, even if the newly added monomer is different that what was used previously. But is the living polymerization still "alive" while it is in that paused, deplete state, or is it more like a dormant state? (Or maybe even a "zombie" state as was discussed yesterday?) I guess polymer scientists and engineers have a hard time distinguishing between "live" and "dead". But then again, I have wondered that about my colleagues themselves at times too, so perhaps the misuse is understandable.

Previous Years

April 30, 2014 - Dow Chemical Keeps Plodding Along and Silencing Critics

April 30, 2012 - Another Set of Rants about a Rejected SBIR Grant

April 30, 2010 - Natureworks

April 30, 2010 - This Changes Everything!

April 30, 2009 - Skip the ER for potential heart attacks and find a spectroscopist instead

April 30, 2009 - This isn't even peer-reviewed